This paper proposed a new algorithm named GSP-K, which is a peer caching algorithm based on global segment popularity for P2P VoD system. This algorithm evaluates the cache utility of media segment via gathering the statistics of media segment popularity globally, and makes the numbers of a media segment copies in the whole system vary directly with it’s cache utility. The simulation experiments indicated that GSP-K algorithm has better performance in increasing statistics precision of segment popularity, cache space utilization rate and segment hit radio than others algorithms such as LRU, LFU and LRU-K.